Geological map of the Catalan agate-amethyst minig district (Artigas department, Republica Oriental del Uruguay).

In the Catalan mining district (Artigas Department, Uruguay) agate and amethyst are exploited in the basalts of the Arapey Formation (Early Cretaceous). From 1996 to 1999, the Authors executed investigations in the Catalan for the EU project “Programa de cooperaciòn entre la Comision de comunidades europeas y la Republica Oriental del Uruguay en el sector de las piedras semipreciosas y en el de las rocas ornamentales: Proyecto de apoyo para la planificacion territorial y la salvaguardia del medio ambiente (YRYB73011,N95,019)”. Photo-interpretation, Landsat TM5 satellite images processing and a geological survey allowed to realise a geological map (scale 1:50,000) of the Catalan mining district. The map highlights outcropping basalt flows, agate-amethyst mineralized areas and mining sites. In the Catalan, five basalt flows outcrop (cI÷cV). While the uppermost portions of the flows cII and cIII are mineralized and actually exploited, mineralization of cI, cIV and cV is less developed or absent. The geometric relationships among cI, cII and cIII suggest that the morphology of cI controlled and prevented the spread toward south-southeast of the lavas of cIII (and probably of cII). As a consequence the Catalan mining district can not extend to south-southeast beyond the extent of the flows cII and cIII.